1. Field of the Invention
The present invention relates to an engine provided with an oil circulation path and a cooling fluid path.
2. Description of the Prior Art
Briefly giving a description of an oil circulation path of a general engine, oil sucked by an oil pump from an oil reservoir within a crankcase or an oil tank is supplied to each of lubrication points of the engine, for example, a bearing of a crank shaft, a crank pin, a piston, a cam shaft(s) of a cylinder head, and a transmission shaft(s) and the like, via an oil passage for supplying the oil, and is used for lubricating and/or cooling in the lubrication points. Further, the oil after being supplied (used) is returned to the oil reservoir or the oil tank via an oil passage for returning. Such an oil circulation path is described, for example, in Japanese Patent No. 3668460 and the like. Further, in order to positively lower a temperature of the oil after being supplied (used), there is a structure in which an oil cooler is provided in a midstream of the oil circulation path.
Next, briefly giving a description of a cooling fluid path, in the case of a vehicle, a cooling fluid such as cooling water or the like cooled within a radiator is sucked by a water pump, is supplied to a cooling fluid jacket (or a cooling fluid gallery) of a cylinder and a cylinder head via a cooling fluid passage for supplying the cooling fluid, and is supplied (used) for cooling the cylinder and the cylinder head. The cooling fluid after being supplied (after being used) is returned to the radiator via a thermostat and the like, for example, from an upper end portion of the cylinder head, and is cooled. A cooling fluid path with such circulation type is described, for example, in Japanese Patent No. 3392851 and the like. Further, in a case of marine vessels such as personal water craft and the like, water and the like force fed from a portion near an impeller is supplied to an engine via a pipe and the like, and cools an exhaust system (near an exhaust port) of the engine. Further, a part of the water is discharged overboard for test water, and a rest of the water is mixed into an exhaust gas in the exhaust passage via a double tube portion of the exhaust system so as to be discharged overboard.
In a conventional engine provided with the oil circulation path and the cooling fluid path, the oil after being supplied (after being used) is cooled by the oil cooler and the like as mentioned above. On the other hand, the cooling fluid after being used is cooled by the radiator and the like in a circulation type, and is discharged in a disposable type. In other words, there is not provided a structure in which the cooling fluid is positively used for cooling the oil in an inner portion of the engine.